Priming with rocuronium accelerates the onset of neuromuscular blockade

Study Objective: To investigate the effects of priming rocuronium on the time course of neuromuscular blockade. Design: Prospective, controlled, randomized clinical study. Setting: University teaching hospital. Patients: 42 ASA physical status I and II patients undergoing peripheral surgery with general anesthesia. Interventions: Following a standardized propofol- fentanyl induction, patients in Group 1 (n = 21) received a priming dose of rocuronium 0.06 mg/kg followed two minutes later by an intubating dose of rocuronium 0.54 mg/kg. Patients in Group 2 (n = 21) received a saline placebo injection followed two minutes later by rocuronium 0.6 mg/kg. Anesthesia was maintained with isoflurane and nitrous oxide 60% in oxygen. Measurements and Main Results: Neuromuscular function was assessed at the wrist using mechanomyography with a single-twitch mode of stimulation at a frequency of 1 Hz until tracheal intubation and at 0.1 Hz thereafter. The times from injection of the intubating dose of rocuronium until 95% suppression of the twitch tension (onset time), recovery of twitch tension to 25% of control (clinical duration of action), and the time from 25% to 75% spontaneous recovery of twitch tension (recovery index) were recorded. The trachea was intubated at 95% depression of the twitch tension and the intubating conditions were graded using a 3-point scale. The onset times with priming rocuronium (34 ± 6 s) were significantly shorter (p < 0.01) than those without priming 59 ± 14 s). The intubation conditions were similar in the two groups; however, the intubating times with priming were significantly shorter. The clinical duration of action and the recovery index did not differ significantly between the two groups. Conclusions: Priming rocuronium decreased the onset times and thus, the intubating times without increasing the clinical duration of action or recovery index.